Rack fastening for free-piston units



March 2, 11946. l R. J. HOOKER 2,437,025

RACK FASTENING FOR FREE PIsTQN' UNITS Filed May 11, 1946 2 Sheets-Sheet 1 i n @e 8 n I N In E t v *t O 0 O Q0 D- (D'O O 0 0 O) O) D O 0 vr O) 0 (O *f o) lC D 0 E w l i D TD w 8 l o' I X 0 o O E O) OJ al @O @C o c w 0 9. 0 OJ 'f INVENTOR l 3 RALPH .1. HOOKER I l ATTORNEY Mrch z, 194s.v R, J, HOOKER 2,437,026

RACK FA'STENING FOR FREE PISTON UNITS Filed May l1, 1946 2 Sheets-Sheet 2 FIGB y l ,B

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INVENTOR RALPH ,1. HOOKER ATTORNEY- Patented Mar. 2, 1948 RACK FASTENING FOR FREE-PISTON UNITS Ralph J. Hooker, Manchester, Conn.,assignor to United Aircraft Corporation, East Hartford, Conn., a corporation of Delaware Application May 11, 1946, Serial No. 669,089

8 Claims. (Cl. 123-46) In the operation of opposed piston types of freepiston units the pistons are caused to move symmetrically by a linkage which interconnects the opposed piston assemblies. This linkage in many cases consists of racks projecting from the pistons and engaging with an interconnecting pinion. The racks are guided adjacent to the pinion to maintain the teeth properly in mesh and the racks are also rigidly mounted inthe pistons. A slight mis-alignment of the rack mounting in the piston with the rack guide adjacent to pinion may cause bending of the rack thereby increasing the loads on the piston and also causing excessive wear on the racks. A feature of this invention is an arrangement by which to permit lateral movement of the rack in the piston to correct for such mis-alignment.

The loads on the piston assemblies are generally balanced by using a pair Tof restraining linkages located on opposite sides of the axis of the pistons. When this is done the tolerances in dimension of the racks may cause Isuch a variation in the positions of the piston engaging the end of the racks that a bending load will be applied to the piston. A feature of this invention is a rack fastening that will avoid this diiiculty by adjusting the axial position of support of the rack within the piston. Another feature` is a structure that permits the axial adjustment without affecting the desired lateral movement of the rack within the piston.

In the opposed piston types of free-piston units the opposed pist-on assemblies must be accurately located with respect to the center of the unit. A feature of the invention is a rack fastening that permits adjustment of the position of the piston with respect to the center of the engine thereby obtaining the desired relative positions of the opposed piston assemblies.

Other objects and advantages will be apparent from the specication and claims', and from the accompanying drawings which illustrate an embodiment of the invention.

Fig. 1 is a sectional view through the freepiston unit.

Fig. 2 is a sectional view along the line 2-2 `of Fig, 1.

Fig. 3 is a fragmentary section View on a larger scale through the rack fastening in the compresser piston.

Fig. 4 is a perspective view of the piston assemblies showing a pair of synchronizing linkages, and Fig. 5 is an enlarged sectional View of one of the compressor valves.

With reference to Fig. l the free-piston unit discharged through exhaust ports 58 includes an engine cylinder Il! having reciprocating pistons I2 and I4 to which compressor pistons I6 and I8 in cylinders 20 and 22 are integrally connected. Sleeves 24 and 2B attached to the compressor pistons complete the reciprocating piston assemblies. The sleeves in combination with stationary pistons 28 and 36 from'air spring cylinders.

The piston assemblies are moved apart by the burning of fuel linjected into engine cylinder vIll through one or more nozzles 32. Air compressed in the air spring cylinder on the power stroke returns the 'piston assemblies. The assemblies are always maintained at equal distances from the center of the engine cylinder by one or more linkages which, as shown, include rack-s `:i4 and 36 extending inwardly from the opposed compressor pistons and meshing with a centrally located pinion 3,8. As'shown in Fig.y 2, the racks are guided adjacent to the pinion by bores 40 in the housing 4| that supports the pinion. Although only one linkage is shown it is frequently desirable to use a pair of linkages located on opposite sides of the longitudinal axis of the unit to avoid undesirable bending moments on the piston assemblies. f

Intake manifold 42, which extends around the compressor and engine cylinders, conducts air to intake valves 44 in the heads of the compressor cylinders through which air alternately enters opposite ends of the cylinders. The compressed air leaves the cylinders through discharge valves 46 also at opposite ends of the compressor cylinders and passes into a center scavenge chamber 48 and end chambers 50 and 52. These chambers may be interconnected by a scavenge manifold not shown. The valves may be constructed as shown in the co-pending Cronstedt et al. application,'Serial No. 495,933, now Patent No, 2,410,428, dated November 5, 1946.

Compressed gas from the scavenge chambers enters ports 54 and 56 which are uncovered by pistons I2 and I4 at the end of the power stroke thereby permitting air to be blown through the engine cylinder. Gas in the engine cylinders is into an exhaust manifold 60.

The racks are guided by the bores 40 and, if the rack mountings in the compressor pistons are not accurately aligned with these bores, the racks may bind in the bores and the bending loads on the pistons may be enough to cause failure of the piston. To avoid this, as shown in Fig. 3, the fastening for the rack is designed to permit a limited amount of lateral movement of the rack within the piston. The compressor piston itil/has a bore 62 therein which receives a cylindrical projection B4 on the rack 36. As shown, the cylindrical projection 64 is `somewhat smaller in diameter than the bore B2 to permit the rack to move laterally. A radial flange 66 on the rack limits the endwise movement of the rack with respect to the piston. To hold the rack in position a cap E8 is threaded to a plug 10 which may also be threaded into the end of the rack 36. The cap 68 has a cylindrical surface 12 Which is the same diameter as the outer surface of the cylindrical projection 64 and which is aligned with the projection 64 when the parts are in the operative position shown. The cap 68 carries a. radial iiange 'I4 located within a recess 16 in the piston and limiting the endwise movement of the rack in the piston.

The flanges 65 and 14 may engage with opposite,

. against turning within the end of the rack by a pin 16 and the cap $8 is locked on the plug by a Cotter pin or other fastening means 18.

In assembly of a free-piston unit, the precise position of the opposed piston assemblies may be controlled by the use of the spacer rings Sii positioned between the flanges 55 and 'M and the adjacent parts of the compressor piston. The thickness of these spacers may be selected so that the axial position of the piston assembly may be adjusted with respect to the end of the rack. Where there is more than one linkage thesespacers 80 may also be used to compensate for any build-up of manufacturing tolerances so that the rack loadings will be evenly distributed and so that there will be no bending moment applied to the piston assemblies through the unequal dimensions in the linkages. t will be apparent that these spacers 80 may be provided in only one of the rack fastenings or may be used for all of the fastenings. In either event the cap 'I6 is so proportioned that its inner end surfaces 82 will engage with the end surfaces 8d of the rack before the flanges 66 and 'i4 can bind on the spacers 80 on the piston to prevent the desired lateral movement of the rack.

It is to be understood that the invention is not limited to the specic embodiment herein illustrated and described, but may be used in other ways Without departure from its spirit as dened by the following claims.

I claim:

1. In a free-piston unit, opposed piston assemblies, a rod projecting from each assembly and means interconnecting said rods to cause said assemblies to move symmetrically with respect to the center of the unit, in combination with means for supporting each rod in the piston assembly to provide for a limited amount of la*- eral movement Within the piston assembly, said means including a bore in the piston assembly larger in diameter than the rod.

2. In a free-piston unit, opposed piston assemblies,ia rod projecting from each assembly and means interconnecting said rods to cause said assemblies toV move symmetrically with respect to the center of the unit, in combination with means for supporting .each rod in the piston assembly to provide for a limited amount of symmetrically, each of said racks being guided adjacent to the pinion, in combination with means forsupporting each rack in the piston assembly to provide for a limited amount of lateral movement of the rack in the assembly.

4. In a free-piston unit, opposed piston assemblies including engine pistons and compressor pistons movable therewith a rack projecting from each piston assembly and a pinion interconnecting said racks to cause said assemblies to move symmetrically each of said racks being guided adjacent to the pinion, in combination with means for supporting each rack in the compressor piston to provide for a limited amount of lateral movement of the rack Within the compressor piston.

5. In a free-piston unit, opposed piston assemblies including engine pistons and compressor pistons movable therewith a rack projecting from each piston assembly and a pinion interconnecting said racks to cause said assemblies to move symmetrically, each of said racks being guided adjacent to the pinion, in combination with means for supporting each rack in the compressor piston to provide for a limited amount of lateral movement of the rack within the compressor piston, said means including a bore in the compressor piston larger in diameter than the rack, and means for limiting the axial movement or the rack in Vsaid bore.

6. In a free-piston unit, opposed piston assemblies including engine pistons and compressor pistons movable therewith, a rack projecting from each piston assembly and a pinion interconnecting said racks to cause said assemblies to move symmetrically, each of said racks being guided adjacent to the pinion, in combination with means for supporting each rack in the compressor piston to provide for a limited amount of lateral movement of the rack within the compressor piston, said means including a bore in the compressor piston larger in diameter than the rack and in which the end of the rack is positioned, a ilange on said rack engageable axially with the compressor piston, and a cap on the end of the rack also engaging axially with the compressor piston on the opposite side from the ange on the rack.

7. In a free-piston unit, opposed piston assemblies including engine pistons and compressor pistons movable therewith a rack projecting from each piston assembly and a pinion interconnecting said racks to cause said assemblies to move symmetrically, each of said racks being guided adjacent to the pinion in combination with means for supporting each rack in the compressor piston to provide for a limited amount of lateral movement of the rack within the compressor piston said means including a bore in the compressor piston larger in diameter than the rack and in which the end of the rack is positioned, a iiange on said rack engageable axially with the compressor piston and a cap on the end of the rack having a ilange engaging axially with the side of the compressor piston opposite to the ited amount of lateral movement of the rack 10 within the piston assembly said means including a bore in the piston assembly larger in diameter than the rack and in which the end of the rack is positioned and spaced anges carried by the rack for limiting the axial movement of the rack 15 2,064,913

6 within the piston assembly and spacer rings positioned between the least one of the vanges and the adjacent piston surface for controlling the axial position of the rack within the piston.

RALPH J. HOOKER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,112,368 Janicke Mar. 29, 1938 2,139,425 Steiner Dec. 6, 1938 Hedges Dec. 22, 1936 

